1. Field of the Invention
The present invention relates generally to heat exchangers for motor vehicles and, more specifically, to a folded tube and method for making same for a heat exchanger in a motor vehicle.
2. Description of the Related Art
It is known to provide a tube for a heat exchanger such as a condenser in an air conditioning system of a motor vehicle. The tube typically carries a first fluid medium in contact with its interior while a second fluid medium contacts its exterior. Typically, the first fluid medium is a liquid and the second fluid medium is air. Where a temperature difference exists between the first and second fluid mediums, heat will be transferred between the two via heat conductive walls of the tube.
It is also known to provide corrugated fins or ribs in the interior of the tube to increase the surface area of conductive material available for heat transfer to cause turbulence of the fluid carried in the interior of the tube and to increase the burst strength of the tube. One known method of making such a tube is to physically insert a corrugated fin into the generally flattened tube after the tube has been manufactured. This is an extremely difficult process since the corrugated fin to be inserted into the tube is extremely thin and subject to deformation during the insertion process.
Another known method of forming a tube for a heat exchanger is to extrude the tube in an extrusion process. In this construction, internal ribs are formed during the extrusion. However, these extruded tubes are relatively expensive to produce.
Yet another known method of forming a tube for a heat exchanger is to provide a flat, elongated sheet with lugs and the ends of the sheet are folded to form the tube. The ends of the tube are then brazed. An example of such a tube is disclosed in U.S. Pat. No. 5,386,629. In this construction, the tube may have flow paths between the lugs having a hydraulic diameter of less than 0.050 inches. Hydraulic diameter is conventionally defined as the cross-sectional area of each of the flow paths multiplied by four and divided by a wetted perimeter of the corresponding flow path. While a hydraulic diameter of less than 0.050 inches optimizes heat transfer efficiency, it is relatively expensive to produce.
Although the above tubes have worked well, they suffer from the disadvantage that the extruded tubes are relatively costly to manufacture Another disadvantage of the above tubes is that the lugs are not folded and squeezed. Yet another disadvantage of the above tubes is that the hydraulic diameter of the flow paths are not greater than 0.050 inches, making them relatively expensive to produce. Therefore, there is a need in the art to provide a folded tube for a heat exchanger of a motor vehicle that overcomes these disadvantages.